1. Field of the Invention
The present invention relates to a fluid purifying apparatus that includes a reactor that purifies a purifying target fluid such as waste liquid by applying pressure and heat to the purifying target liquid while mixing an oxidant such as air with the purifying target fluid and decomposing organic matter contained in the purifying target fluid through an oxidation reaction.
2. Description of the Related Art
A method of conducting biological treatment using an activated sludge has been generally used as a method for purifying liquid wastes such as human waste, sewage, domestic wastewater from residential areas, livestock excreta, and effluents from food processing factories. However, the method is not conducive to treating liquid wastes containing a high-concentration organic solvent, which impede activities of microorganisms in the activated sludge, without reducing the concentration, or treating liquid wastes containing fine particles of non-biodegradable plastics. Also, the method is not conducive to treating waste liquids containing a high content of persistent organic matter such as oil that cannot be easily decomposed by microorganisms.
Meanwhile, technological developments are recently being made with respect to a fluid purifying apparatus that purifies waste liquid by applying heat and pressure to a mixed fluid of the liquid waste and an oxidant such as air, and decomposing organic matter contained in the mixed fluid through oxidative decomposition. An example of such a fluid purifying apparatus is disclosed in Japanese Laid-Open Patent Publication No. 2001-9482 (referred to as “Patent Document 1” hereinafter). The fluid purifying apparatus applies heat and pressure to the mixed fluid of waste liquid and air inside a reactor and causes water contained in the mixed fluid to be in a supercritical state. Supercritical water has properties between those of liquid and gas. Supercritical water is created under a condition where the temperature is raised above the critical temperature of water and the pressure is raised above the critical pressure of water. In the reactor, organic matter may be hydrolyzed in a mixture of supercritical water and air, or organic matter may undergo oxidative decomposition in the presence of oxygen.
By implementing such a technique that involves oxidative decomposition of organic matter contained in a mixed fluid by applying a high temperature and a high pressure to water contained in the mixed fluid and converting the water into supercritical water, purification may be performed on waste liquids that could not be purified through biological treatment such as waste liquids containing a high concentration of organic solvent, waste liquids containing plastic particles, and waste liquids containing persistent organic matter, for example.
The inventors of the present invention are developing a new fluid purifying apparatus that is capable of inducing oxidative decomposition of organic matter in a reactor by applying a pressure that is lower than the critical pressure of water to a mixed fluid while heating the mixed fluid to a high temperature so that the water contained in the mixed fluid is turned into a high-temperature and high-pressure vapor state. The inventors have found through their research and development efforts that such a fluid purifying apparatus is also capable of purifying waste liquids containing a high concentration of organic solvent, waste liquids containing plastic particles, and waste liquids containing persistent organic matter, for example.
However, in the case of purifying a waste liquid containing a high content of inorganic suspended solids as the purifying target fluid using the above-described fluid purifying apparatus or the fluid purifying apparatus disclosed in Patent Document 1, for example, cleaning operations that involve halting operations of the fluid purifying apparatus to clean the interior of the reactor have to be frequently conducted.
Specifically, conventional reactors include a vertical type reactor such as that illustrated in FIG. 1 of Patent Document 1, and a horizontal type reactor such as that illustrate in FIG. 2 of Patent Document 1. The vertical type reactor is arranged to have its longitudinal side extend in a substantially vertical direction. The vertical type reactor is configured to receive waste liquid from its upper side, decompose organic matter contained in the waste liquid while mixing an oxidant with the waste liquid and transporting the waste liquid from the upper side towards the lower side, and discharge the purified fluid to a drain pipe that is connected to the lower end of the tank. The horizontal type reactor is arranged to have its longitudinal side extend in a substantially horizontal direction. The horizontal type reactor is configured to receive waste liquid from one of its horizontal ends, decompose organic matter contained in the waste liquid while the mixing an oxidant with the waste liquid and transporting the waste liquid from the one horizontal end to the other horizontal end, and discharge the purified fluid to a transfer pipe that is connected to the other horizontal end.
In either of the above types of reactors, water contained in the waste liquid is converted into supercritical water or high-temperature and high-pressure vapor immediately after the waste liquid is introduced into the reactor. In this case, a large amount of inorganic suspended solids contained in the waste liquid are precipitated, and the inorganic solids settle and accumulate at the bottom of reactor. In the vertical type reactor, the inorganic solids accumulated at the bottom of the reactor may clog the drain pipe connected to the lower end of the reactor to thereby hinder effective transfer of the supercritical water or high-temperature and high-pressure vapor within the reactor. In the horizontal type reactor, precipitation of the inorganic solids occurs largely near the one horizontal end from which the waste liquid is introduced. Thus, eventually, the inorganic solids may pile up from the bottom to the ceiling of the tank at the one horizontal end to thereby clog the tank itself. In such case, it may be difficult to effectively transfer the supercritical water or the high-temperature and high-pressure vapor within the reactor from the one horizontal end to the other horizontal end. Thus, operations of the fluid purifying apparatus have to be halted on a frequent basis to conduct cleaning operations on the reactor.
In view of the above, suspended solids may be removed in advance through coagulation, sedimentation, or sieving, for example, to reduce the concentration of inorganic suspended solids contained in the waste liquid. In this way, the amount of precipitation of inorganic solids within the reactor may be reduced and the frequency rate at which cleaning operations have to be conducted may be reduced. However, removing suspended solids in advance may preclude efficient use of the decomposition energy of organic matter contained in the waste liquid and costs may be raised as a result.
Specifically, suspended solids contained in waste liquid may generally be divided into inorganic suspended solids and organic suspended solids. When removal processes such as coagulation, sedimentation, or sieving is performed, the inorganic suspended solids as well as the organic solids are removed. Organic suspended solids may be dissolved into supercritical water or high-temperature and high-pressure vapor under a high temperature and a high pressure and may be oxidized and decomposed thereafter, or even if the organic suspended solids are separated from water and precipitated as organic solids, they may be burned in the presence of oxygen. Thus, organic suspended solids are not likely to be accumulated within the reactor. Accordingly, even if a large amount of organic suspended solids exist within the reactor, the organic suspended solids are not likely to contribute to clogging of the reactor. Moreover, because organic suspended solids generate heat upon undergoing oxidative decomposition within the reactor, they may contribute to maintaining the temperature within the reactor at a high temperature so that heating energy for heating the reactor by heating means such as a heater may be conserved. Thus, removing the organic suspended solids before introducing the waste liquid into the reactor may have a detrimental effect of increasing the heating energy required within the reactor which may in turn lead to a cost increase.